The only documentation I can find for DetectMobileDevice comes from Direct upgrading from 4.4 to 4.7 page.

In site.ini documentation page, it's important to create proper information for:

[SiteAccessSettings]
    DetectMobileDevice
    MobileSiteAccessURL
    MobileSiteAccessList[]
    MobileDeviceFilterClass

It's also important to explain how this feature works with eZP 5.x, namely if it's necessary to have legacy_mode: true set in ezpublish.yml for bot siteaccess: the normal and the mobile one.

From what I saw, this will work only in legacy_mode.

Finally, Direct upgrading from 4.4 to 4.7 is wrong.

When upgrading from eZ Publish 4.6 to 4.7 and you are using eZ Flow, you can benefit from the new mobile device detection feature. Put the following settings in your "settings/override/site.ini.append.php" file:

[SiteAccessSettings]
 [...]
 DetectMobileDevice=enabled
 MobileSiteAccessURL=http://example.com/iphoneMobileSiteAccessList[]
 MobileSiteAccessList[]=iphone
 [...]

This settings do not need to be set in settings/override/site.ini.append.php, as the documentation says, but can be set for each siteaccess allowing different mobile sites (what is good for languages).

 MobileSiteAccessURL=http://example.com/iphoneMobileSiteAccessList[]

The line above has a typo

MobileSiteAccessURL=http://example.com/iphone
MobileSiteAccessList[]